Method for preparing silver nanowire with high length-diameter ratio in one step through solvothermal synthesis reaction

Abstract

The invention relates to a silver nanowire preparation technology, and aims to provide a method for preparing a high-length-diameter-ratio silver nanowire in one step through a solvothermal synthesis reaction. Comprising the following steps: mixing and stirring silver ions and a PVP (Polyvinyl Pyrrolidone) solution, continuously adding bromide ions and chloride ions serving as a nucleating agent, and mixing and stirring to obtain a reaction solution; transferring the reaction solution into a hydrothermal reaction kettle, and reacting under a heating condition to obtain a silver nanowire mother solution; and sediments in the silver nanowire mother liquor are separated and cleaned, and the silver nanowires with the length-diameter ratio being 2148-3190 are obtained. By means of a cooperative regulation mechanism of bromide ions, chloride ions and polyvinylpyrrolidone, the problem that in existing research work, the length and the diameter of the silver nanowire are difficult to consider at the same time is solved, and it is ensured that the length of the silver nanowire is maintained while the diameter of the silver nanowire is reduced; the technological process is simplified, and the problems of nitrogen atmosphere reaction, secondary heating and the like in the prior art are solved; and by optimizing all reaction parameters, stable and controllable preparation of the silver nanowire with the high length-diameter ratio is finally achieved.

Description

Technical Field

[0001] The present invention relates to a silver nanowire preparation technology, and in particular to a simple preparation method for silver nanowires with a high aspect ratio. Background Art

[0002] With the development of science and technology, flexible electronic products, with their softness, portability, and wide-area applicability, have been widely used in flexible optoelectronics, energy, and sensor devices. As core components of flexible electronic products, flexible transparent conductive films that combine flexibility, high transmittance, and electrical conductivity have gradually become a research hotspot in this field. A large amount of research has been carried out on transparent conductive materials such as indium tin oxide (ITO), carbon nanotubes, graphene, metal meshes, and silver nanowires (AgNWs). Indium tin oxide (ITO) is a widely used transparent conductive material in the flexible electronics industry. However, its inherent brittleness, resource scarcity, and high cost make it difficult to meet the application needs of new flexible electronic components. Compared with several other transparent conductive materials, silver nanowires, with their nanometer size effect, low resistance, high transmittance, low cost, and large-scale printing production, are expected to become the best choice to replace ITO.

[0003] The resistance and transmittance of silver nanowire transparent conductive films are closely related to the length and diameter of the silver nanowires. Since the film resistance primarily comes from the contact resistance between the silver nanowires, longer silver nanowires can effectively reduce overlap, thereby lowering the overall resistance of the transparent conductive film. Furthermore, as the diameter of the silver nanowires decreases, the light transmittance gradually increases, resulting in higher transparency. Therefore, synthesizing silver nanowires with a high aspect ratio is key to improving the performance of silver nanowire transparent conductive films. Methods for synthesizing silver nanowires include soft and hard templates, microwave-assisted synthesis, wet chemical methods, solvothermal methods, and polyol methods. Patent Publication No. CN110355359A discloses a polyol-based synthesis route for ultrafine silver nanowires. This method can achieve an average silver nanowire diameter of approximately 13 nm, but the maximum length of the resulting silver nanowires is only 16 μm. Furthermore, this method requires heating the reaction mixture to the reaction temperature under a nitrogen atmosphere, followed by cessation of aeration and a closed reaction, which increases the operational complexity. Patent publication number CN11895237A discloses a method for preparing ultra-long silver nanowires, using a seed growth method to ultimately produce silver nanowires several hundred microns long. This method first involves reacting the raw materials at 110-170°C for 2-3 hours to produce seed crystals. Ethylene glycol is then preheated to 110-170°C, followed by the addition of a nucleation inhibitor, polyvinyl pyrrolidone, and a seed solution, which are then mixed thoroughly. Silver nitrate solution is then added to the mixture using a syringe pump, and after the reaction, ultra-long silver nanowires are obtained. While this method can produce ultra-long silver nanowires, the operation is cumbersome and unsuitable for large-scale production. Patent publication number CN117259771A discloses a method for producing high aspect ratio silver nanowires using a double heating method. First, a template and a reducing agent are stirred and dissolved at 80-110°C. A control agent and a silver salt solution are then added and allowed to react until the mixture turns reddish-brown. The reaction solution was heated to 140-160° C. for a second time and reacted for 1.5 h to obtain silver nanowires.

[0004] The aforementioned research reveals that achieving both ultrafine diameter and high length during silver nanowire synthesis has become a technological challenge. Furthermore, the complex and cumbersome operations of some preparation processes are major limitations on the large-scale production of silver nanowires. Therefore, developing a synthesis method that balances both diameter and length while maintaining a simple and efficient process flow to produce high aspect ratio silver nanowires that meet the performance requirements of flexible transparent electrodes is crucial for the large-scale application of silver nano-transparent conductive films. Summary of the Invention

[0005] The technical problem addressed by this invention is to overcome the current shortcomings of silver nanowire synthesis, which hinder the balance between nanowire diameter and length, as well as the complex process flow. This method provides a one-step method for preparing high-aspect-ratio silver nanowires through a solvothermal synthesis reaction. By optimizing and precisely controlling process parameters, this method achieves a one-step, controllable synthesis of high-aspect-ratio silver nanowires, increasing their length while reducing their diameter, simplifying the process flow, and improving process stability.

[0006] In order to solve the problems in the existing silver nanowire synthesis process, the solution of the present invention is:

[0007] A method for preparing high aspect ratio silver nanowires in one step by a solvent thermal synthesis reaction is provided, comprising:

[0008] After mixing and stirring a silver ion solution and a polyvinylpyrrolidone (PVP) solution, a bromide ion solution and a chloride ion solution as a nucleating agent are added, and the mixture is stirred to obtain a reaction solution; the reaction solution is transferred to a hydrothermal reactor and reacted under heating conditions to obtain a silver nanowire mother liquor; and the sediment in the silver nanowire mother liquor is separated and cleaned to obtain silver nanowires with an aspect ratio of 2148 to 3190.

[0009] As a preferred embodiment of the present invention, the silver ion solution is a silver nitrate solution using ethylene glycol as a solvent.

[0010] As a preferred embodiment of the present invention, the polyvinyl pyrrolidone (PVP) solution is obtained by adding PVP to ethylene glycol and stirring at 70° C. for 4 hours.

[0011] As a preferred embodiment of the present invention, the chloride ion solution uses ethylene glycol as a solvent, and the solute is any one of sodium chloride, copper chloride, ferric chloride, and cobalt chloride.

[0012] As a preferred embodiment of the present invention, the bromide ion solution is a sodium bromide solution using ethylene glycol as a solvent.

[0013] As a preferred embodiment of the present invention, when preparing each solution and reaction solution, the stirring speed is controlled to be 600-750 r / min.

[0014] As a preferred embodiment of the present invention, in the reaction solution, the molar ratio of silver ions to polyvinylpyrrolidone (PVP) is 1:(2-3.4), and the molar ratio of silver ions: bromide ions: chloride ions is 500:(0.8-1):1.

[0015] As a preferred embodiment of the present invention, the reaction conditions in the hydrothermal reactor are: reaction temperature 140-155° C., reaction time 4 h, and the amount of reaction solution added is more than 80% of the reactor volume.

[0016] As a preferred embodiment of the present invention, the sediment is separated and cleaned by the following method: ethanol is added to the silver nanowire mother liquor to dilute it, and the upper liquid is removed after centrifugation; the sediment is dispersed with the same volume of ethanol and then centrifuged to remove the supernatant, and the operation is repeated 4 to 5 times to finally obtain the silver nanowire product.

[0017] As a preferred embodiment of the present invention, the diameter of the silver nanowires is 21 to 27 nm, and the length is 55 to 67 μm.

[0018] Description of the invention principle:

[0019] The present invention adopts a solvent thermal synthesis reaction method to prepare high aspect ratio silver nanowires in one step, and the length and diameter of the silver nanowires are synergistically regulated by chloride ions, bromide ions and polyvinyl pyrrolidone. In the process of preparing the reaction solution, the silver ions are first mixed with polyvinyl pyrrolidone to make the silver ions uniformly dispersed in polyvinyl pyrrolidone (PVP), and then the chloride ions and bromide ions synergistically react with the silver salt to form an insoluble precipitate, which is used to suppress the reduction rate of the silver ions in the early stage of the reaction, avoid the explosive nucleation of silver, and reduce the initial particle size of the silver grains. In the early stage of the growth of the silver nanowires, the free bromide ions in the reaction solution can quickly adsorb on the (110) crystal plane, making up for the initial coating deficiency caused by the large molecular weight of polyvinyl pyrrolidone, thereby suppressing the lateral growth of the silver nanowires and promoting the one-dimensional longitudinal growth of the silver nanowires. By regulating the filling amount of the reaction solution in the reactor, the air content in the closed reaction system can be controlled. The oxygen in the air can promote the reaction of ethylene glycol to generate glyoxal, improve the reduction rate, thereby reducing the reaction time and lowering the reaction temperature, and realizing the synthesis of high-quality silver nanowires without nitrogen. In addition, the present invention achieves precise control of the micromorphology of silver nanowires by synergistically regulating the reaction temperature, the amount of polyvinyl pyrrolidone used, and the amount of bromide ions used, simplifies the process flow, and ultimately develops a one-step simple method for synthesizing high aspect ratio silver nanowires.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention uses chloride ions, bromide ions, and polyvinyl pyrrolidone to synergistically regulate the micromorphology of silver nanowires. The introduction of bromide ions not only coordinates with chloride ions to regulate the size of the initial silver grains, but also coordinates with polyvinyl pyrrolidone to regulate the growth of the silver nanowires during the initial reaction, inhibiting lateral growth and promoting the one-dimensional longitudinal growth of the silver nanowires. By leveraging the synergistic regulation mechanism of bromide ions, chloride ions, and polyvinyl pyrrolidone, the present invention overcomes the difficulty in balancing the length and diameter of silver nanowires in existing research, ensuring that the length of the silver nanowires is maintained while reducing the diameter of the silver nanowires.

[0022] 2. The present invention controls the air content in the closed reaction system by regulating the loading amount of the reaction solution, thereby promoting the reaction of ethylene glycol to form glyoxal, simplifying the process flow, and overcoming the problems of the existing process such as the need for nitrogen atmosphere reaction and secondary heating.

[0023] 3. This invention achieves high-aspect-ratio silver nanowires that meet the performance requirements of flexible transparent electrodes by synergistically controlling the reaction temperature, polyvinyl pyrrolidone dosage, and bromide ion dosage. By optimizing various reaction parameters, the stable and controllable preparation of high-aspect-ratio silver nanowires is ultimately achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 and Figure 2 This is a scanning electron microscope photograph of the silver nanowires prepared in Example 1.

[0025] Figure 3 and Figure 4 This is a scanning electron microscope photograph of the silver nanowires prepared in Example 2.

[0026] Figure 5 and Figure 6 This is a scanning electron microscope photograph of the silver nanowires prepared in Example 3.

[0027] Figure 7 and Figure 8 This is a scanning electron microscope photograph of the silver nanowires prepared in Example 4.

[0028] Figure 9 This is a scanning electron microscope photograph of the reaction product of Comparative Example 1.

[0029] Figure 10 This is a scanning electron microscope photograph of the silver nanowires prepared in Comparative Example 2.

[0030] Figure 11 This is a scanning electron microscope photograph of the reaction product of Comparative Example 3.

[0031] Figure 12 This is a scanning electron microscope photograph of the silver nanowires prepared in Comparative Example 4.

[0032] Figure 13 This is a scanning electron microscope photograph of the silver nanowires prepared in Comparative Example 5.

[0033] Figure 14 This is a scanning electron microscope photograph of the silver nanowires prepared in Comparative Example 6.

[0034] Figure 15 This is a scanning electron microscope photograph of the silver nanowires prepared in Comparative Example 7. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0036] 1. Overview of the technical solution of the present invention

[0037] The present invention provides a method for preparing high aspect ratio silver nanowires in one step by solvent thermal synthesis reaction, comprising:

[0038] 1. Preparation of various solutions:

[0039] Silver ion solution, polyvinylpyrrolidone (PVP) solution, chloride ion solution, and bromide ion solution were prepared under stirring conditions using ethylene glycol as solvent. The PVP solution was prepared by stirring at 70°C for 4 hours, while the other solutions were prepared by stirring at room temperature.

[0040] As an example, the concentration of the silver ion solution is 8.3 g / L, and the solute is silver nitrate; the solute in the chloride ion solution is any one of sodium chloride, copper chloride, iron chloride, or cobalt chloride, and the concentration is 20 mmol / L; the concentration of the bromide ion solution is 20 mmol / L, and the solute is sodium bromide. The concentration of the PVP solution is 12.5 g / L, and the molecular weight of the PVP used is 1,300,000.

[0041] 2. Prepare reaction solution

[0042] After the silver ion solution and the polyvinyl pyrrolidone (PVP) solution are mixed and stirred, the bromide ion solution and the chloride ion solution as a nucleating agent are added, and the mixture is mixed and stirred to obtain a reaction solution.

[0043] Specifically, a silver ion solution and a polyvinylpyrrolidone (PVP) solution were first mixed and stirred for 10 minutes. Then, a chloride ion solution and a sodium bromide solution were added while stirring, and the mixture was mixed and stirred for another 10 minutes to obtain a reaction solution. In the reaction solution, the molar ratio of silver ion to polyvinylpyrrolidone (PVP) was 1:(2-3.4), and the molar ratio of silver ion:bromide ion:chloride ion was 500:(0.8-1):1.

[0044] When preparing the above solutions and reaction solutions, control the stirring speed to 600-750 r / min.

[0045] 3. Thermal synthesis reaction

[0046] The reaction solution was transferred to a hydrothermal reactor and reacted at a temperature of 140-155° C. for 4 hours; the amount of reaction solution added was more than 80% of the volume of the reactor, and a silver nanowire mother liquor was obtained after the reaction.

[0047] Under laboratory conditions, a 25 mL hydrothermal reactor can be selected.

[0048] 4. Separate and clean the products

[0049] Ethanol was added to the silver nanowire mother liquor at a volume ratio of 10 times to dilute it, and the upper liquid was removed after centrifugation; the sediment was dispersed with the same volume of ethanol and then centrifuged to remove the supernatant, and the operation was repeated 4 to 5 times to finally obtain the silver nanowire product.

[0050] As an optional example, the speed is set to 1000 r / min and the time is set to 10 minutes during each centrifugation. The diameter of the silver nanowire is 21-27 nm, the length is 55-67 μm, and the aspect ratio after conversion and rounding is 2148-3190.

[0051] 2. Examples and Comparative Examples

[0052] Example 1

[0053] A simple one-step method for preparing high aspect ratio silver nanowires comprises the following steps:

[0054] (1) Weigh 0.083 g of silver nitrate and dissolve it in 10 mL of ethylene glycol. Stir at 600 rpm at room temperature until the solution is homogeneous and no solid is visible to the naked eye, thereby obtaining a silver nitrate solution.

[0055] (2) Weigh 0.125 g of polyvinylpyrrolidone (Mw = 1300000) and dissolve it in 10 mL of ethylene glycol. Stir the mixture at 70 °C and 600 rpm for 4 h to obtain a PVP solution.

[0056] (3) Weigh 0.0584 g of sodium chloride and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 600 r / min until the solution is uniform to obtain a sodium chloride solution. Weigh 0.102 g of sodium bromide and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 600 r / min until the solution is uniform to obtain a sodium bromide solution.

[0057] (4) Measure 10 mL of silver nitrate solution and place it in a 50 mL beaker. Place the beaker on a stirring platform and adjust the speed to 700 rpm. Then, add 10 mL of PVP solution to the silver nitrate solution at a volume ratio of silver nitrate solution to PVP solution = 1:1, and mix and stir for 10 minutes.

[0058] (5) While keeping the rotation speed unchanged, 50 μL of sodium chloride solution and 50 μL of sodium bromide solution were further added to the mixed solution obtained in step (4) according to the volume ratio of silver nitrate solution: sodium chloride solution: sodium bromide solution = 200:1:1, and the mixture was stirred for 10 minutes to prepare a reaction solution; after conversion, the molar ratio of silver ion to polyvinylpyrrolidone (PVP) in the reaction solution was 1:2, and the molar ratio of silver ion: bromide ion: chloride ion was 500:1:1.

[0059] (6) 20 mL of the reaction solution prepared in step (5) was measured and transferred to a 25 mL hydrothermal reactor. The reaction temperature was set to 140° C. and the reaction was carried out for 4 h to obtain a silver nanowire mother solution.

[0060] (7) Add 200 mL of ethanol to the silver nanowire mother liquor at a volume ratio of silver nanowire mother liquor to ethanol = 1:10, transfer the diluted silver nanowire mother liquor to a 500 mL centrifuge bottle, set the centrifugal speed to 1000 r / min, and the time for 10 min. After centrifugation, remove the upper liquid, disperse the sediment with 200 mL of ethanol, and continue centrifugation;

[0061] (8) Repeat the centrifugation operation of step (7) 4 to 5 times to obtain silver nanowires with high aspect ratio.

[0062] The micromorphology of the silver nanowires prepared by this method is as follows Figure 1 and Figure 2 As shown, the characteristic data of the nanowires were statistically analyzed using the particle size analysis software NanoMeasurer, and the results were: the nanowire length was about 60 μm, the diameter was about 23 nm, and the aspect ratio was calculated to be 2608. The characteristic data of the nanowires in the following examples and comparative examples were all obtained in this way.

[0063] Example 2

[0064] A method for preparing a high-thickness and toughness silane protective coating comprises the following steps:

[0065] (1) Weigh 0.083 g of silver nitrate and dissolve it in 10 mL of ethylene glycol. Stir at room temperature at 650 rpm until the solution is homogeneous and no solid is visible to the naked eye, thereby obtaining a silver nitrate solution.

[0066] (2) Weigh 0.125 g of polyvinylpyrrolidone (Mw = 1300000) and dissolve it in 10 mL of ethylene glycol. Stir at 70 °C and 650 r / min for 4 h to obtain a PVP solution.

[0067] (3) Weigh 0.27 g of ferric chloride and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 650 r / min until the solution is uniform to obtain a ferric chloride solution. Weigh 0.102 g of sodium bromide and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 650 r / min until the solution is uniform to obtain a sodium bromide solution.

[0068] (4) Measure 10 mL of silver nitrate solution and place it in a 50 mL beaker. Place the beaker on a stirring platform and adjust the speed to 750 rpm. Then, add 15 mL of PVP solution to the silver nitrate solution at a volume ratio of silver nitrate solution to PVP solution = 1:1.5, and mix and stir for 10 minutes.

[0069] (5) While keeping the rotation speed unchanged, 50 μL of ferric chloride solution and 40 μL of sodium bromide solution were added to the mixed solution obtained in step (4) according to the volume ratio of silver nitrate solution: ferric chloride solution: sodium bromide solution = 200:1:0.8, and the mixture was stirred for 10 minutes to prepare a reaction solution; after conversion, the molar ratio of silver ion to polyvinylpyrrolidone (PVP) was 1:3.4, and the molar ratio of silver ion: bromide ion: chloride ion was 500:0.8:1.

[0070] (6) 21 mL of the reaction solution prepared in step (5) was measured and transferred to a 25 mL hydrothermal reactor. The reaction temperature was set to 150° C. and the reaction was carried out for 4 h to obtain a silver nanowire mother solution.

[0071] (7) Add 200 mL of ethanol to the silver nanowire mother liquor at a volume ratio of silver nanowire mother liquor to ethanol = 1:10, transfer the diluted silver nanowire mother liquor to a 500 mL centrifuge bottle, set the centrifugal speed to 1000 r / min, and the time for 10 min. After centrifugation, remove the upper liquid, disperse the sediment with 200 mL of ethanol, and continue centrifugation;

[0072] (8) Repeat the centrifugation operation of step (7) 4 to 5 times to obtain silver nanowires with high aspect ratio.

[0073] The micromorphology of the silver nanowires prepared by this method is as follows Figure 3 and Figure 4 As shown, the nanowire length is about 67 μm, the diameter is about 21 nm, and the aspect ratio is 3190.

[0074] Example 3

[0075] A method for preparing a high-thickness and toughness silane protective coating comprises the following steps:

[0076] (1) Weigh 0.083 g of silver nitrate and dissolve it in 10 mL of ethylene glycol. Stir at 600 rpm at room temperature until the solution is homogeneous and no solid is visible to the naked eye, thereby obtaining a silver nitrate solution.

[0077] (2) Weigh 0.125 g of polyvinylpyrrolidone (Mw = 1300000) and dissolve it in 10 mL of ethylene glycol. Stir the mixture at 70°C and 700 rpm for 4 h to obtain a PVP solution.

[0078] (3) Weigh 0.238 g of cobalt chloride and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 600 r / min until the solution is uniform to obtain a cobalt chloride solution. Weigh 0.102 g of sodium bromide and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 600 r / min until the solution is uniform to obtain a sodium bromide solution.

[0079] (4) Measure 10 mL of silver nitrate solution and place it in a 50 mL beaker. Place the beaker on a stirring platform and adjust the speed to 700 rpm. Then, add 12 mL of PVP solution to the silver nitrate solution at a volume ratio of silver nitrate solution to PVP solution = 1:1.2, and mix and stir for 10 minutes.

[0080] (5) While keeping the rotation speed unchanged, 50 μL of cobalt chloride solution and 45 μL of sodium bromide solution were further added to the mixed solution obtained in step (4) according to the volume ratio of silver nitrate solution: cobalt chloride solution: sodium bromide solution = 200:1:0.9, and the mixture was stirred for 10 minutes to prepare a reaction solution; after conversion, the molar ratio of silver ion to polyvinylpyrrolidone (PVP) in the reaction solution was 1:2.8, and the molar ratio of silver ion: bromide ion: chloride ion was 500:0.9:1.

[0081] (6) 23 mL of the reaction solution prepared in step (5) was measured and transferred to a 25 mL hydrothermal reactor. The reaction temperature was set to 155° C. and the reaction was carried out for 4 h to obtain a silver nanowire mother solution.

[0082] (7) Add 200 mL of ethanol to the silver nanowire mother liquor at a volume ratio of silver nanowire mother liquor to ethanol = 1:10, transfer the diluted silver nanowire mother liquor to a 500 mL centrifuge bottle, set the centrifugal speed to 1000 r / min, and the time for 10 min. After centrifugation, remove the upper liquid, disperse the sediment with 200 mL of ethanol, and continue centrifugation;

[0083] (8) Repeat the centrifugation operation of step (7) 4 to 5 times to obtain silver nanowires with high aspect ratio.

[0084] The micromorphology of the silver nanowires prepared by this method is as follows Figure 5 and Figure 6 As shown, the nanowire length is about 65 μm, the diameter is about 26 nm, and the aspect ratio is 2500.

[0085] Example 4

[0086] A method for preparing a high-thickness and toughness silane protective coating comprises the following steps:

[0087] (1) Weigh 0.083 g of silver nitrate and dissolve it in 10 mL of ethylene glycol. Stir at room temperature at 650 rpm until the solution is homogeneous and no solid is visible to the naked eye, thereby obtaining a silver nitrate solution.

[0088] (2) Weigh 0.125 g of polyvinylpyrrolidone (Mw = 1300000) and dissolve it in 10 mL of ethylene glycol. Stir at 70 °C and 650 r / min for 4 h to obtain a PVP solution.

[0089] (3) Weigh 0.134 g of copper chloride and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 650 r / min until the solution is uniform to obtain a copper chloride solution. Weigh 0.102 g of sodium bromide and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 650 r / min until the solution is uniform to obtain a sodium bromide solution.

[0090] (4) Measure 10 mL of silver nitrate solution and place it in a 50 mL beaker. Place the beaker on a stirring platform and adjust the speed to 750 rpm. Then, add 13 mL of PVP solution to the silver nitrate solution at a volume ratio of silver nitrate solution to PVP solution = 1:1.3, and mix and stir for 10 minutes.

[0091] (5) While keeping the rotation speed unchanged, 50 μL of copper chloride solution and 40 μL of sodium bromide solution were further added to the mixed solution obtained in step (4) according to the volume ratio of silver nitrate solution: copper chloride solution: sodium bromide solution = 200:1:0.8, and the mixture was stirred for 10 minutes to prepare a reaction solution; after conversion, the molar ratio of silver ion to polyvinylpyrrolidone (PVP) in the reaction solution was 1:3, and the molar ratio of silver ion: bromide ion: chloride ion was 500:0.8:1.

[0092] (6) 20 mL of the reaction solution prepared in step (5) was measured and transferred to a 25 mL hydrothermal reactor. The reaction temperature was set to 140° C. and the reaction was carried out for 4 h to obtain a silver nanowire mother solution.

[0093] (7) Add 200 mL of ethanol to the silver nanowire mother liquor at a volume ratio of silver nanowire mother liquor to ethanol = 1:10, transfer the diluted silver nanowire mother liquor to a 500 mL centrifuge bottle, set the centrifugal speed to 1000 r / min, and the time for 10 min. After centrifugation, remove the upper liquid, disperse the sediment with 200 mL of ethanol, and continue centrifugation;

[0094] (8) Repeat the centrifugation operation of step (7) 4 to 5 times to obtain silver nanowires with high aspect ratio.

[0095] The micromorphology of the silver nanowires prepared by this method is as follows Figure 7 and Figure 8 As shown, the nanowire length is about 58 μm, the diameter is about 27 nm, and the aspect ratio is 2148.

[0096] Example 5

[0097] A method for preparing a high-thickness and toughness silane protective coating comprises the following steps:

[0098] (1) Weigh 0.083 g of silver nitrate and dissolve it in 10 mL of ethylene glycol. Stir at room temperature at 650 rpm until the solution is homogeneous and no solid is visible to the naked eye, thereby obtaining a silver nitrate solution.

[0099] (2) Weigh 0.125 g of polyvinylpyrrolidone (Mw = 1300000) and dissolve it in 10 mL of ethylene glycol. Stir at 70 °C and 650 r / min for 4 h to obtain a PVP solution.

[0100] (3) Weigh 0.134 g of copper chloride and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 650 r / min until the solution is uniform to obtain a copper chloride solution. Weigh 0.102 g of sodium bromide and dissolve it in 50 mL of ethylene glycol. Stir at room temperature at 650 r / min until the solution is uniform to obtain a sodium bromide solution.

[0101] (4) Measure 10 mL of silver nitrate solution and place it in a 50 mL beaker. Place the beaker on a stirring platform and adjust the speed to 750 rpm. Then, add 13 mL of PVP solution to the silver nitrate solution at a volume ratio of silver nitrate solution to PVP solution = 1:1, and mix and stir for 10 minutes.

[0102] (5) While keeping the rotation speed unchanged, 50 μL of copper chloride solution and 50 μL of sodium bromide solution were further added to the mixed solution obtained in step (4) according to the volume ratio of silver nitrate solution: copper chloride solution: sodium bromide solution = 200:1:0.8, and the mixture was stirred for 10 minutes to prepare a reaction solution; after conversion, the molar ratio of silver ion to polyvinylpyrrolidone (PVP) in the reaction solution was 1:2, and the molar ratio of silver ion: bromide ion: chloride ion was 500:1:1.

[0103] (6) 20 mL of the reaction solution prepared in step (5) was measured and transferred to a 25 mL hydrothermal reactor. The reaction temperature was set to 140° C. and the reaction was carried out for 4 h to obtain a silver nanowire mother solution.

[0104] (7) Add 200 mL of ethanol to the silver nanowire mother liquor at a volume ratio of silver nanowire mother liquor to ethanol = 1:10, transfer the diluted silver nanowire mother liquor to a 500 mL centrifuge bottle, set the centrifugal speed to 1000 r / min, and the time for 10 min. After centrifugation, remove the upper liquid, disperse the sediment with 200 mL of ethanol, and continue centrifugation;

[0105] (8) Repeat the centrifugation operation of step (7) 4 to 5 times to obtain silver nanowires with high aspect ratio.

[0106] The silver nanowires prepared by this method have a length of about 55 μm, a diameter of about 25 nm, and an aspect ratio of 2200.

[0107] Comparative Example 1

[0108] The reaction temperature is 130°C, except that the reaction temperature is 140°C in step (6) of Example 1 is replaced by the reaction temperature of 130°C. The rest is the same as in Example 1. The obtained product is as follows: Figure 9 As shown, due to the low reaction temperature, the reducing ability in the reaction system is reduced, which ultimately leads to the generation of a large number of particles after the reaction, and no nanowires are formed.

[0109] Comparative Example 2

[0110] The step (5) of Example 1 was adjusted to add the nucleating agent solution alone without adding the sodium bromide solution. The rest was the same as in Example 1. The reaction product was as follows: Figure 10 As shown in the figure, due to the lack of sodium bromide solution, the silver nuclei were not efficiently coated in the initial nucleation stage, resulting in the aggregation and growth of the initial silver nuclei. This solution can form nanowires with good morphology, but the enlargement of the initial nuclei results in a thicker silver nanowire diameter of approximately 120nm.

[0111] Comparative Example 3

[0112] The step (5) of Example 1 was adjusted by adding sodium bromide solution alone without adding nucleating agent solution. The rest was the same as Example 1. The reaction product was as follows: Figure 11 As shown in the figure, since no nucleating agent solution was added, the initial silver ion precipitate was insufficient, the reduction rate increased, and some crystal nuclei began to grow without being effectively coated, resulting in the final products being mainly nanoparticles and short rods.

[0113] Comparative Example 4

[0114] The "measure 20 mL" in step (6) of Example 1 was replaced by "measure 10 mL", and the rest was the same as in Example 1. The obtained product was as follows Figure 12 As shown in the figure, as the loading decreases, the air content in the reaction system increases, the ethylene glycol reduction rate accelerates, and the reducing power of the entire reaction system is significantly enhanced. Although the synergistic effect of chloride and bromide ions can reduce the reduction rate of the system, the initial crystal nuclei grow rapidly, resulting in larger initial crystal nuclei. The final product can form silver nanowires, but the diameter of the silver nanowires is approximately 118nm.

[0115] Comparative Example 5

[0116] The "silver nitrate solution: PVP solution = 1:1" in step (4) of Example 1 was replaced with "silver nitrate solution: PVP solution = 1:3", and the rest was the same as in Example 1. The obtained product was as follows: Figure 13 As shown in the figure, as the amount of PVP solution increases, the competitive adsorption between polyvinylpyrrolidone (PVP) molecules increases, causing its crystal face selectivity to weaken or even fail. This in turn causes radial growth during the growth of silver nanowires, resulting in a coarsening of the final product diameter and an increase in degradation.

[0117] Comparative Example 6

[0118] The reaction temperature is 140°C in step (6) of Example 1, and the reaction temperature is 160°C. The rest is the same as in Example 1. The obtained product is as follows: Figure 14 As shown in the figure, silver nanowires can form at this temperature, but they exhibit significant degradation, such as fusion and abnormal diameter increase. This phenomenon occurs because the increased reaction temperature significantly enhances the surface diffusion of silver ions, resulting in a sufficient lattice and causing fusion of the nanowires upon contact. Furthermore, the increased temperature accelerates Ostwald ripening, intensifies the dissolution of small particles, increases the number of free silver ions, and some diffuses to the radial surface and deposits, ultimately leading to an abnormal increase in the diameter of the silver nanowires.

[0119] Comparative Example 7

[0120] Silver nanowires were prepared according to the method reported in the literature (DOI: 10.1039 / c7ra13683h). Figure 15 As shown in the figure, the diameter of the silver nanowires prepared by this method is generally above 100nm and is relatively thick. The main reason is that this method only uses sodium chloride as a nucleating agent to control the growth of the silver nanowires, resulting in a large initial nucleus and ultimately a coarsening of the silver nanowire diameter.

[0121] It can be seen from the final product morphology and analysis data of the above embodiments and comparative examples that the preparation process of the present invention is simple, easy to operate, and does not require secondary heating; the synergistic effect of chloride ions and bromide ions is used to avoid the explosive nucleation of silver and reduce the initial particle size of the silver grains; by the coordinated regulation of bromide ions and polyvinyl pyrrolidone, the lateral growth of silver nanowires is inhibited and the one-dimensional longitudinal growth of silver nanowires is promoted, thereby achieving the reduction of the diameter of the silver nanowires while taking into account the length; by regulating the reaction solution filling amount and controlling the air content in the closed reaction system, high-quality silver nanowires can be synthesized without nitrogen; by synergistically optimizing the reaction temperature, the amount of polyvinyl pyrrolidone used, and the amount of bromide ions used, the micromorphology of the silver nanowires is precisely controlled, and ultimately the stable and controllable preparation of silver nanowires with a high aspect ratio is achieved.

[0122] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing high aspect ratio silver nanowires by a solvothermal synthesis reaction in one step, characterized in that: include: After mixing and stirring the silver ion solution and the polyvinyl pyrrolidone (PVP) solution, a bromide ion solution and a chloride ion solution as a nucleating agent are added, and the mixture is stirred to obtain a reaction solution; The reaction solution is transferred to a hydrothermal reactor and reacted under heating conditions to obtain a silver nanowire mother solution; Separate and clean the sediment in the silver nanowire mother liquor to obtain silver nanowires with an aspect ratio of 2148 to 3190.

2. The method according to claim 1, characterized in that The silver ion solution is a silver nitrate solution using ethylene glycol as a solvent.

3. The method according to claim 1, characterized in that The polyvinyl pyrrolidone (PVP) solution is obtained by adding PVP to ethylene glycol and stirring at 70° C. for 4 hours.

4. The method according to claim 1, wherein The chloride ion solution uses ethylene glycol as a solvent, and the solute is any one of sodium chloride, copper chloride, ferric chloride, and cobalt chloride.

5. The method according to claim 1, wherein The bromide ion solution is a sodium bromide solution using ethylene glycol as a solvent.

6. The method according to claim 1, characterized in that When preparing each solution and reaction solution, control the stirring speed to 600-750 r / min.

7. The method according to claim 1, characterized in that In the reaction solution, the molar ratio of silver ions to polyvinylpyrrolidone (PVP) is 1:(2-3.4), and the molar ratio of silver ions: bromide ions: chloride ions is 500:(0.8-1):

1.

8. The method according to claim 1, characterized in that The reaction conditions in the hydrothermal reactor are: reaction temperature 140-155° C., reaction time 4 h, and the amount of reaction solution added is more than 80% of the reactor volume.

9. The method according to claim 1, characterized in that The sediment was separated and cleaned by the following method: ethanol was added to the silver nanowire mother liquor for dilution, and the upper liquid was removed after centrifugation; the sediment was dispersed with the same volume of ethanol and the supernatant was removed by centrifugation, and the operation was repeated 4 to 5 times to finally obtain the silver nanowire product.

10. The method according to any one of claims 1 to 9, characterized in that The diameter of the silver nanowire is 21-27 nm, and the length is 55-67 μm.

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